1. Field of the Invention
The present invention relates to an optical disc drive, and more particularly to an optical disc being drive adapted to write data to, and/or read data from, optical disc being different in format from each other, such a compact disc (CD), digital video disc or digital versatile disc (DVD), etc. According to the present invention, a plurality of light sources is disposed apart from each other radially of such an optical disc and a laser light is emitted from one of the light sources selected according to the type of optical disc loaded in the optical disc drive towards the optical disc and focused through a common optical system for the different types of optical discs. Thus, a single optical pickup can be used in common with such a plurality of optical discs without any deterioration of the optical property.
2. Description of the Related Art
The conventional optical disc drive or CD player is adapted to irradiate a laser beam from an optical pickup onto an information recording surface of a CD and process a detection result of a return light from the CD surface to read or reproduce a variety of data recorded in the CD.
The conventional optical pickups include a type having a light source and photodetector disposed separately therein, and a type using an optical integrated device consisting integrally of light source and photodetector. The U.S. Pat. Nos. 4,873,429 and 4,733,067 disclose examples of the construction of the optical pickups of the latter type. This type of optical pickup can be designed more compact and have a higher reliability.
It is considered that using such an optical integrated device to build the optical pickup also in an optical disc drive for DVD, a so-called DVD player, for example, the DVD player can be designed compact and simple. A DVD player designed to write data to, and/or read data from, a CD as well will be very conveniently usable.
In this case, by forming an optical integrated device integrally from a light source and photodetector for DVD and a light source and photodetector for CD, an optical disc player capable of writing data to, and/or reading data from, both CD and DVD can be provided.
When the optical integrated device is constructed as in the above and an objective lens is commonly used with both DVD and CD, either of the light source for DVD or that for CD will be disposed off the optical axis of the objective lens. The laser beam emitted from the light source thus disposed off the optical axis will be incident obliquely to the objective lens. As a result, the obliquely incident laser beam will have an increased aberration and thus the optical property will be deteriorated.
As defined in the standard, the pit depth in the compact disc (CD) is one eighth (xcex/8) of the wavelength xcex of the laser beam irradiated to the CD, while the pit depth in the DVD is one fourth (xcex/4) of the wavelength xcex of the laser beam irradiated to the DVD. Thus, in the DVD player, it is difficult to detect a tracking error signal by the similar method to that for CD. Namely, tracking error signal has to be produced by the so-called differential phase detection (DPD) method, for example. In this DPD method, the laser diode as light source has to be disposed in such a manner that the deflection plane of the laser beam will be parallel or perpendicular to the scanning direction of the laser beam.
For effective utilization of the internal space of the optical integrated device, the laser diode should desirably be disposed in such a manner that the deflection plane of the laser beam will be parallel or perpendicular to the direction of the optical path of the laser beam.
However, when the laser beam deflection plane is directed as in the above, the optical property of a read signal from the optical disc will be deteriorated.
It is therefore an object of the present invention to overcome the above-mentioned drawbacks of the prior art by providing an optical pickup simply constructed and having a plurality of light sources selectively used to write data to, and/or read data from, an optical recording medium without any deterioration of optical property, and an optical disc drive using the optical pickup.
According to the present invention, there is provided an optical disc drive
adapted to read information from an optical disc by emitting a laser beam from a selected one of a plurality of light sources disposed apart from each other radially of the optical disc and focusing the laser beam on the optical disc, detecting a return light resulted from reflection of the laser beam at the optical disc and processing the result of return light detection, the optical disc drive including:
a common optical system for irradiating the laser beam emitted from the selected one of the plurality of light sources to the optical disc; and
a moving means operative in response to a laser beam output from the selected light source to move all or a part of the optical system radially of the optical disc.
According to the present invention, there is also provided an optical pickup adapted to irradiate a laser beam to an optical recording medium, detect a return light from the optical recording medium and providing a result of return light detection, the optical pickup including:
first and second light sources to emit the laser beams of different wavelengths, respectively;
a photodetector to detect the return light from the optical recording medium; and
an optical system to converge the laser beam emitted from a selected one of the first and second light sources and guide the return light from the optical recording medium to the photodetector;
the first and second light sources being disposed so that the directions of the deformation, caused by the astigmatism, of the sectional shape of the laser beams emitted from the light sources will nearly coincide with each other; and
the optical system being adapted for common use with the laser beams emitted from the first and second light sources, and including an astigmatism correcting means for common use with the laser beams emitted from the first and second light sources.
According to the present invention, there is also provided an optical disc drive adapted to read information from an optical disc by emitting a laser beam from a selected one of a plurality of light sources disposed apart from each other radially of the optical disc and focusing the laser beam on the optical disc, detecting a return light resulted from reflection of the laser beam at the optical disc and processing the result of return light detection, the optical disc drive including:
first and second light sources to emit the laser beams of different wavelengths, respectively;
a photodetector to detect the return light from the optical recording medium; and
an optical system to converge the laser beam emitted from a selected one of the first and second light sources and guide the return light from the optical recording medium to the photodetector;
the first and second light sources being disposed so that the directions of the deformation, caused by the astigmatism, of the sectional shape of the laser beams emitted from the light sources will nearly coincide with each other; and
the optical system being adapted for common use with the laser beams emitted from the first and second light sources, and including an astigmatism correcting means for common use with the laser beams emitted from the first and second light sources.